FIELD OF THE INVENTION
The present invention relates to a flame retardant electrically insulating compound that does not evolve toxic or corrosive gases as it burns. Such compounds are especially suited for use as insulation or sheathing for electrical wires and cables.
High rise buildings, power stations, various industrial plants, transit systems, such as subways and ships, are especially vulnerable to fire hazard. Due to the large number of people and the limited exits found in such environments, severe loss of life can occur in the event of a fire. Furthermore, if large amounts of smoke are generated exits and exit routes are obscured, loss of life occurs which would have been avoided if no such smoke condition had prevailed and rapid evacuation had thus been possible.
Additionally, fire can spread along wire or cable, especially in duct systems. Smoke and the harmful gaseous ignition products of a fire or smoldering material can be transported through, for example, air conditioning systems or subway tunnels and cause health hazards in areas remote from the original point of ignition.
Corrosion obviously causes severe damage to equipment. A fire in a telephone exchange, for example, can cause loss of life of people not involved at the fire site, due to corrosion induced failure of telephone, alarm and control systems and the subsequent loss of ability to contact emergency services.
Thus, there is a need for insulation and sheathing materials for wires and cables that are self extinguishing and which do not evolve toxic or corrosive gases or large amounts of smoke. Furthermore, fungal attack can occur in the confined, damp conditions in which such wires and cables are installed, particularly in transit systems and ships.
Resin compositions which do not evolve toxic and corrosive gases and have anti-fungal properties are described in U.S. Pat. No. 4,871,787.
A common problem which occurs with such resin compositions is that the incorporation of large amounts of metal hydroxides into polymeric materials has a deleterious effect on the tensile elongation of the resin compositions compared to the unmodified base polymers. Due to this low elongation, cracking and tearing of the insulation or sheath can take place during both installation and use.
A further effect is that the viscosity of such metal hydroxide loaded resin compositions is so high that they are very difficult to form into the final object. Slower extrusion rates and specialized high pressure equipment are required, especially when compared to flame retardant, low smoke compositions based on poly(vinyl chloride) polymers.
Thus, flame retardant commercial resin compositions known to the art which contain metal hydroxides generally compromise one or more of their properties to optimize one or more of the others. Such compromises could be avoided if it were possible to significantly reduce the amount of metal hydroxide present without reducing the flame retardancy of the resulting resin composition.